Muscle wasting is a serious complication of catabolic diseases such as chronic kidney disease (CKD) and contributes substantially to the morbidity and mortality of patients. We have evidence that accelerated muscle protein degradation in CKD patients and animals is due to an increase in muscle protein degradation and a decrease in muscle regeneration. In addition, CKD leads to a sharp increase in collagen deposition and fibrosis in regenerating (injured) muscles of mice. All three consequences of CKD (protein degradation, regeneration and fibrosis) are associated with down-regulation of microRNA-29 (miR29). Specifically, we found that 1) PTEN and FoxO3A, two proteins that are involved with protein degradation, were up-regulated in muscle from CKD animals; 2) YY1, a protein that inhibits muscle cell differentiation, is increased in CKD muscle; and 3) there was a 3-fold decrease in miR29 in the muscle of CKD mice. This microRNA will inhibits PTEN, FoxO3A, YY1 and multiple collagens post-transcriptionally according computer predicted analysis. A decrease in miR29, therefore, should result in increased PTEN and activated FoxO3A proteins which would contribute to increased protein degradation. A lower level of miR29 should also increase the inhibition of myogenesis by increasing YY1 and promote muscle fibrosis by up-regulating collagen gene expression in injured muscles of CKD mice. It is unclear whether decreased miR29 will promote collagen mediated fibrosis in the uninjured CKD mice. Our proposed research will determine if these changes are, as we believe, responsible for a large amount of the muscle loss observed in catabolic disease. We will study the effect of miR29 on the components of PI3K/PTEN/Akt/atrogin-1 signaling pathway in the muscle of CKD and non- CKD mice. We will test the hypothesis that an increase in miR29 promotes muscle cell differentiation and prevents fibrosis by down-regulation of YY1 and collagens in MyoDcreRosa26tm1Sor mice. We will use in vivo gene transfer of miR29 by lentivirus and electroporation to test our theory. We anticipate finding that: 1) in normal animals, miR29 regulates PTEN, YY1 and multiple collagens by directly interacting with the 3'-UTR of their mRNAs and affecting them on a post-transcription level; 2) in CKD, increased miR29 prevents accelerated muscle protein degradation, promotes muscle regeneration and attenuates injured-induced muscle fibrosis, three hallmarks in the muscle of this disease. These results should provide new approaches for developing therapeutic strategies to correct muscle wasting in catabolic disease. PUBLIC HEALTH RELEVANCE: Muscle wasting is a serious complication of catabolic diseases such as chronic renal failure (CKD), diabetes, cancer and heart failure. It contributes substantially to patient mortality. We have evidence that muscle loss is due to an increase in muscle protein degradation and a decrease in muscle regeneration. Both of these mechanisms of muscle loss are related to a down- regulation of microRNA-29 (miR29). Our proposal will determine if a decrease in miR29 causes these changes, and whether increasing miR29 will reverse these changes. Data from these studies should provide new approaches for developing therapeutic strategies to correct muscle wasting in catabolic disease.